Investigation of Interference fit and its effect on fatigue life in hardened steel

In this study, interference fit process and its influence on fatigue life of holed specimens made of AISI4340 hardened steel were investigated experimentally. For this purpose, Tungsten carbide pins were fitted into the steel samples and putted under fatigue test with zero load ratio and 10 Hz frequency. These experiments were done for specimens with 5 interfence levels and two repetition. Results revealed that the compressive force required for interference fitting the pin in hole increases as the interference size goes up. The peak force was observed when the pin reached bottom of specimen and the maximum plastic deformation occurred. 3D finite element modeling of interference fit showed that distribution of residual stress on the hole wall and far away from it were compressive and tensile respectively. Moreover, results of fatigue experiments showed increasing the specimens fatigue life up to 1.5% interference fit. In this level, fatigue life is 2.5 times greater than specimen without fitting. However, by increasing interference up to 2%, increasing trend of fatigue life is stopped. Analysis the fracture surface of samples showed that the fatigue cracks are initiated from edge of the hole at specimens with press fit. While crack initiation site was in the middle plane of hole for specimens without fitting.